Hi @Kotryna,
I have a couple of suggestions about the SILVA reference database.
- Update to the latest pre-made SILVA classifiers. If needed, you can train the classifiers yourself using these files.
- Use RESCRIPt to make your own SILVA reference database.
As for filtering away organelle / plastid sequences, see the documentation here.
Also, this information may help too.
-Cheers!
-Mike